I just recently put in a motor in a 95 Nissan Sentra. The car runs great but going down the road sometimes the car revs up and down by itself, not a whole lot but it annoying. I ran the self diagnostic test and got the code for the mass air flow sensor and the iac valve. Well, I checked the iac valve and was bad, tried to clean it out with no luck, still doesn't work. My question is this, could that be what's causing the revving problem because the part is 138 dollars. And I'm thinking also maybe the fuel pressure regulator or injector problems. Any advice would be great.

PS, I followed the Haynes manual for checking the IAC valve, I checked for voltage on the correct wire on the connector with the key on, checked good, also pulled out the connector with motor running, no change in anything, then did an ohms test where supposed to on the thing after removing the connector again, didn't meet specs, then tried to make the valve move by applying voltage to it, the thing barely moved, in either direction when tried.

The reason I didn't ask about the mass air flow sensor is because I already changed it out today, I got one from a junkyard, I didn't check it yet however. I will wait till tomorrow afternoon to do that. The new MAF sensor is 200 dollars.

If this helps any its a GLE and has a 1.6 liter engine

I failed to mention that the computer also gave the code for the coolant temperature sensor. I just didn't think that it would have any thing to do with the car doing that, got to looking deeper in my manual and it says that the sensor can affect the fuel injection system. So I'm going to check that this evening and replace if bad. By the way the car isn't over heating or anything. I would still like suggestions if anyone thinks it could still be anything else, I will probably go ahead and order the IAC valve and put it in this weekend too. The coolant temp sensor is only 20 bucks so I'll do that first if it's bad.

Okay I got all the check engine light issues taken care of with new and used sensors. Been test driving it around. No more light, code 55 now, good to go.

Still having the same problem, well, more of an annoyance but for all I know could be a serious problem.

I'm going to try to explain what it's doing a little better now. When driving down the road, it runs great, while accelerating or foot on accelerator. However, when you let off the gas completely, to coast, for example going down the road at 40 miles an hour. The rpms cut back to around 1300, jump back up to around 1800, back and forth back and forth. Please, any help or advice would be great.

If your IAC does not meets specs, that where you should start.

IAC i would think is causing that issue by telling it to open the throttle enough cuz maybe u got a dirty throttle body? not quite sure but i have a MAF problem with mine atm. All it does is misfire like a sob
Got one from the junk yard, ran great for 2 weeks now it's doign it again. put a sensor i knew was good in it, ran good for 30 mins then started. either my known good MAF is bad too cuz it was in the car for those 2 weeks in the back seat but i checked all my wires and found no voltage drops and less than .5 ohms of resistance on all wires from MAF to ECM. Signal voltage looks great while it's doing it's thing so i would think ECM but when u unplug the MAF it is good so im trying to figure out how good input and good output (i think) is working like it does

does anyone know how to get in touch with the orignal poster of this thread I have been having the same problem with the revving issue and have looked everywhere for an answer. I was wondering if he or she ever got it worked out, and if so how. Do any of you have any more ideas?

With my 1995 Sentra it will rev up and down very quickly sometimes once sometimes twice, but only when coasting or at a complete stop. i can even lightly touch on the the pedal and it will rev itself once or twice, again, very quickly.

I have tried to change the IAC (got one at a juck yard) and then just cleaned the old one I had since the other one did the same. I have sprayed carb cleaner around looking for a vaccume leak, (but I probably dont know where all the lines are) I would really appreiate some ideas.